2:09 AM Visitor?

What is going on around here? At 2:09 am Mark heard someone knocking on our front door. He got up, put his pants on and went out to open the door except there was no one there. Emma had been up barking 3 times during the night each time she would be laying on her bed in the living room, bound up at a run barking at the door but when I would open the door for her to go outside she either wouldn't step outside or would stand right outside the door barking. So in my exhaustion from the night before I refused to get up at 2:09 am.  Mark decided to take Emma outside with him to check around but she cringed by the couch and he actually had to pull her out with him, she is so brave. (NOT) Mark was so spooked he slept the rest of the night with his phone in his pocket just in case he needed to dial 911. Of course we both overslept. Emma is so exhausted she may be too tired to even go on the walk this morning which she loves.